1. Field of the Invention
The present invention relates to systems and methods for performing refractive laser surgery on the eye, and, more particularly, to such systems and methods that modify calculated treatment parameters to achieve an optimal ablation correction.
2. Description of Related Art
In conventional refractive laser surgery, a clinician typically modifies a prescription entered into the treatment system. Such modifications are based upon prior experience with outcomes achieved with that particular treatment system, and also upon experience with particular patient populations derived from, for example, demographic data. For example, a surgeon might enter a 2-diopter myopic treatment prescription for a patient diagnosed with 3 diopters of myopia if analysis of previous outcomes indicates a 50% overcorrection using this system for patients of a particular category. Such an empirical alteration of entered treatment parameters based upon previous experience is referred to as a nomogram adjustment. Nomograms are considered essential by the ophthalmic community because different clinicians employ different surgical techniques, operate under different environmental conditions, have distinct patient demographics, etc.
Conventional surgery involves a limited number of well-defined treatment parameters, principally spherical error, astigmatic error, astigmatic axis, optical zone size, and blend zone size. Thus it is relatively straightforward for a surgeon to develop nomogram formulas based on conventional clinical examinations before and after surgical procedures. In contrast, wavefront-guided customized treatments, such as that disclosed in commonly owned U.S. Pat. No. 6,270,221 B1, the disclosure of which is incorporated herein by reference, involve a complex mathematical description of the pre-operative aberration profile, which is transferred electronically to the treatment system.
In some currently used wavefront-based treatments, the raw wavefront data are modulated to generate a treatment profile in order to account for an apparent radial dependence in the effectiveness of ablative treatment on the corneal tissue. This, however, is currently applied substantially identically in all treatments. At present there is no known convenient method for a surgeon to modify a wavefront-based prescription prior to a procedure such as laser surgery.
In commonly owned patent applications Publication Nos. 2003/0078753 and 2003/0133074, the disclosures of which are incorporated herein by reference, two analytical methods for achieving ablation correction are disclosed based upon previously collected outcomes data.